writeFrame() can have a specific opcode.
Add the PING and PONG opcode support.
Add CLOSE_* constants.
Add the close() method.
Add close() and use getServer() everywhere.
Detect a new protocol error: too big ping message.
Allow empty message in the readFrame message.

Caught it in the upper-level.
Format code. #mania
Detect a new protocol error: empty text frame.
Fix big message (> 0xffff) and code semantics.